CA Foundation · Quantitative Aptitude · Equations
If one root of the equation x² − 9x + k = 0 is twice the other root, what is the value of k?
The value of k is 18. With roots m and 2m, their sum 3m equals 9, so m = 3 and the roots are 3 and 6. The product of the roots equals k, giving 3 × 6 = 18.
- A9
- B18Correct
- C27
- D36
Explanation
Let the roots be m and 2m. Sum = 3m = 9, so m = 3 and the roots are 3 and 6. Product = 3 × 6 = 18 = k. Check: 9 + 18... x² − 9x + 18 = (x − 3)(x − 6). The value 27 would come from wrongly using roots 3 and 9.
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